Commercial navigation applications can be improved by using low cost, small sized navigation grade gyroscopes. Resonator fiber optic gyroscope (RFOG) may be a promising contender for meeting the performance desires for the afore-mentioned commercial navigation applications. In particular, an RFOG has the potential to provide a navigation grade solution with the desired combination of low cost, small package size, and weight. The RFOG uses at least two laser beams, where at least one of the laser beams propagates around a resonator coil in the clockwise (CW) direction and at least one other laser beam propagates around a resonator coil in the counter-clockwise (CCW) direction. In the operation of the RFOG, it is desirable to tune the frequencies of the at least two laser beams to the resonance frequencies of the fiber optic ring resonator. In tuning the frequencies, the resonance frequencies may be measured in the CW and CCW direction. The input beam frequencies may be compared and the difference between the input beam frequencies is proportional to the rotation rate of the resonator coil. However, an indicated output may be present when the gyroscope is not rotating. A measured output when no rotation is present is known as a bias, and the instability of the bias is known as bias instability. Bias instability affects the ability of the RFOG to produce accurate measurements.
One source of bias instability in RFOGs is that the light, used to measure rotation, can propagate within the resonator sensing loop in two polarizations, where the two polarizations of light can be incident on the resonator. When the light is input into the resonator and the light does not entirely couple into only one resonance of the resonator, errors can be produced that cause bias instability. These errors arise because the light that propagates in the two polarization states of the resonator interfere with each other at the gyro output as the fiber changes the difference in refractive index along two axes for the fiber (birefringence).